Foundation posts for highway safety guardrails are typically made of wood or steel, both of which are relatively inexpensive, readily available, and sufficiently strong to support the guardrail.
Recycled plastics are currently in wide use as a compressive structural member xe2x80x9cspacer-blockxe2x80x9d component between a guardrail and post. The plastic spacer block is used as a substitute for the traditional wood or steel spacer block in W-beam highway-roadside guardrail systems. While the concept of using plastics as guard rail post components has been disclosed, plastics generally have not been selected for use in guardrail posts due in part to five structural considerations.
First, the most widely used highway guardrail system is the xe2x80x9cstrong-postxe2x80x9d design. Strong-post guardrail systems resist impacting vehicles in a rigid-manner providing little deflection of the support posts. The standard guardrail posts presently used are 6xe2x80x3 by 8xe2x80x3 timber or 6xe2x80x3 wide-flange steel beams. Both the wood post and the steel post carry the lateral design loadings with very little deflection vis-xc3xa1-vis plastic matrix posts of similar dimensions.
Second, the most widely used guardrail installation method is the xe2x80x9cdrop-hammer.xe2x80x9d The typical truck-mounted guardrail post-driver is a gravity-dead-weight which is dropped on the top of an individual post driving the post into the soil. The post is driven by successive blows of the drop-hammer to the depth desired. Unlike typical foundation pile driving, the guardrail post must be driven to a specific depth as the W-beam rail must be at a specific height above the road surface. Posts in current use that are formed of wood or steel have significant rigidity under the impact of the drop-hammer allowing for transmission of the vertical applied force through the post to the soil matrix. Due to plastic""s significantly higher elasticity, the use of a drop-hammer is impaired as the vertical applied force is dissipated due to the rubbery nature of plastic.
Third, plastics tend to have lower overall tensile and compressive strengths vis-xc3xa1-vis steel. Plastics when dimensioned to that of wood posts still remain inferior in tensile strength. As such, to meet the strength requirements of the standard xe2x80x9cstrong-postxe2x80x9d guardrail post, the dimensional size exceeds the maximum allowable for the typical installation-equipment of the present art.
Fourth, the standard xe2x80x9cstrong-postxe2x80x9d guardrail system requires the use of a xe2x80x9cpost-boltxe2x80x9d (sometimes known as the xe2x80x9cthru-boltxe2x80x9d). The post-bolt is passed through the W-beam rail component, then the spacer-block and finally, through the post. That is, the head of the post-bolt is in contact with the traffic-side of the rail-section and the threaded end of the post-bolt is on the xe2x80x9caway-sidexe2x80x9d of the system""s post. At issue is the incompatibility of a plastic post and the standard steel post-bolt. When the strong-post guardrail is impacted by a crashing vehicle, the W-beam rail and spacer-block and post are usually subjected to torque. The rail, spacer-block, post system resists the applied torque by way of the post-bolt. Due to significant xe2x80x9chardnessxe2x80x9d differential vis-xc3xa1-vis a steel post-bolt and a plastic post, the steel post-bolt tends to knife or cut through the plastic post.
Fifth, a plastic guardrail post, of dimensional size suitable for use with the state-of-the-art installation-equipment, provides significantly less resistance to torque loads due to impacting crashing vehicles.
In one disclosure (U.S. Pat. No. 5,507,473, issued to Hammer et al.), plastic guardrail posts are strengthened by providing a reinforcing member in the plastic extending along a neutral axis of the guardrail post.
The present invention relates to and addresses concerns inherent to plastics virgin and/or recycled) and/or rubber (virgin and/or recycled) and its use as a structural post component, particularly for highway safety guardrails.
A composite foundation post of this invention includes a reinforcement in or attached to the tensile region of a polymer matrix. Preferably, the post is a highway guardrail post, and the reinforcement includes perforated U-channel sheet steel.
In a method of the invention, a drive cap is positioned on the post before the post is driven into a support matrix (e.g., soil).
The present invention offers a number of advantages. The use of reinforcement in the tensile region of the post remedies the lack of tensile strength in the polymer matrix. The use of one or more perforated steel U-channel beams in a highway guardrail post of this invention also imparts strength perpendicular to the run-of-rail but allows the post to shear off if a tire, for example, snags on a post, which would otherwise bring the vehicle and its passenger to a catastrophic stop. Posts of this invention also strongly resist torque so as to minimize xe2x80x9cpocketingxe2x80x9d of the guardrail system when impacted between posts. Further, the polymer matrix can be formed from recycled plastics thereby reducing waste, disposal costs and environmental damage. Moreover, methods of this invention allow the plastic composite post to be driven into the ground without shredding the plastic.